Australia’s inland rivers near a dangerous tipping point

The Barwon-Darling river ecosystem is at a major tipping point, beyond which the natural and agricultural productivity of the system will be diminished in ways that put it beyond recovery.

That’s the sobering message from Professor Martin Thoms, an internationally renowned river scientist from the University of New England (UNE), who has just completed a cutting-edge assessment of river foodwebs in the basin.

Prof. Thoms’s study of snail, mussel and fish specimens collected during the past 130 years is the first of its kind in Australia. His analysis shows that aquatic foodwebs throughout the 650,000 square kilometre Barwon-Darling Basin have changed dramatically in the wake of intense land and water development.

Species that once enjoyed a variety of food sources are now dependent on just algal dominated sources – symptomatic of a loss of resilience throughout the entire basin. And Prof. Thoms thinks it likely that the Murray River system is in a similar state.

“Foodwebs are a major indicator of the composition and health of river communities,” Professor Thoms said.

“This study provides new evidence that foodwebs throughout the entire Barwon-Darling River system have been disturbed and have changed as a result. This has made the system less productive and significantly reduced biodiversity, which has major implications for natural and agricultural ecosystems. Unless we do something fast and new in terms of science or governance we will be unable to restore the basin’s ecological health.”

The recent ground-breaking study, funded by the NSW Environmental Trust, tested the naturally occurring isotope ratios in tissue samples from museum specimens to establish what the snails, mussels and fish were eating in 1860, compared to 1960, when river development quickened. The analysis revealed a growing dependence on algal food sources post-1960.

“Our rivers used to be highly variable, but we have stabilised the flow, creating a better environment for algae to grow and invasive animals like European carp to influence the foodwebs,” said Professor Thoms.

Algae also flourishes on nutrients washed off from farmland, and algal dependence among the river systems’ animals increased in line with accelerated agricultural and water resource development.

“Blue-green algal blooms of the size and magnitude we saw in 1990 are early warning signs, and our study supports this frightening trend.”

Results of the study have major implications for science, policy, and management of land and water resources within the Murray-Darling Basin, which provides 65% of Australia’s irrigated produce.

“Water allocations and the irrigation debate up until now have ignored the simple fact that water is a combined social and ecological resource,” Professor Thoms said. “If the natural productivity of the river declines, then productivity for anyone using the river and floodplain will also decline. Water buy-backs focused only on water ignore the complex relationships between land, vegetation and water. An integrated approach to land-water management of our dryland river systems is desperately needed or productivity will be seriously compromised throughout entire catchments.”

Professor Thoms’ findings are about to be published in the International Journal of Water Resources Research.

In 1996, he was the lead author on a report to the NSW Government and the now-defunct Murray-Darling Basin Commission that forecast many of the issues raised in the July 24 report by ABC’s Four Corners program.

There has been some policy progress over the past 20 years, Prof. Thoms said, but it has been “one step forward, two back”.

Policy ignores risks

Despite billions of dollars being invested in a bid to restore the health of the Murray-Darling Basin, Professor Paul Martin of the Australian Centre for Agriculture and Law at UNE said the monitoring and implementation of current market instruments and regulations is clearly ineffective.

“Bringing rural water use back to sustainable limits in Australia is an enormous challenge,” Professor Martin said.

“But, unfortunately, Australia continues to experience significant failures in the implementation of water policy. Our work has shown that it is the environment and rural communities that bear most of the risks, and that governments consistently under-appreciate the need to manage this.

“It is the quality of that policy implementation and its governance that determines whether public policies work. To make market mechanisms, including the NSW Water Plan, work reliably and fairly requires a far more serious commitment to actually managing the things that can go wrong. Time and time again the less powerful rural communities and the environment suffer the consequences. We need far more integrity in the implementation of natural resource management arrangements, including water management.”